scholarly journals Freezing Method for Rock Cross-Cut Coal Uncovering: Aging Characteristic of Effective Freezing Distance on Injecting Liquid Nitrogen into Coal Seam

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Heyi Ma ◽  
Chuanqu Zhu ◽  
Pengtao Zhao ◽  
Binbin Wang
Keyword(s):  
Thermal Conductivity ◽  
Coal Seam ◽  
Liquid Nitrogen ◽  
Water Injection ◽  
Engineering Practice ◽  
Power Exponent ◽  
Nitrogen Injection ◽  
Artificial Freezing ◽  
Freezing Test ◽  
Aging Characteristic

Based on artificial freezing engineering practice, the comprehensive technology is suggested to realize safe and fast rock cross-cut coal uncovering, which mainly includes four steps of drilling, water injection wetting coal, gas drainage, and injection liquid nitrogen into coal seam. Freezing test of liquid nitrogen injection into coal is carried out to obtain the cooling curves, and comparing the test results, the numerical inverse method is applied to determine the thermal conductivity of coal seam. Then, the model of injecting liquid nitrogen into coal seam is established to simulate and analyze the aging characteristic of effective freezing radius. The results show that the thermal conductivity of wetting coal increases linearly with temperature decreasing. The periodic method with 8h intervals can be adopted to inject liquid nitrogen into coal seam, and the freezing wall is formed around the injection hole. With the increase of freezing time, the effective freezing radius (below 273.15 K) increases by power exponent, and the freezing speed in coal seam decreases gradually. This result will provide a theoretical basis for layout optimization of injection holes in rock cross-cut coal uncovering.

scholarly journals Seepage Law of Injected Water in the Coal Seam to Prevent Rock Burst Based on Coal and Rock System Energy

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Tianwei Lan ◽  
Chaojun Fan ◽  
Hongwei Zhang ◽  
A. S. Batugin ◽  
Luo Ruibin ◽  
...  
Keyword(s):  
Coal Seam ◽  
Coal Mining ◽  
Rock Burst ◽  
Water Injection ◽  
Tectonic Stress ◽  
Energy Concentration ◽  
Engineering Practice ◽  
Principal Stresses ◽  
Rock System ◽  
The Law

Rock burst is one of the typical dynamic disasters in coal mining. In order to reveal the mechanism of rock burst from the energy view point, the relationships between the maximum, minimum, and intermediate principal stresses and the concentration coefficients of the gravity stress k1, k2, and k3 are determined through the geostress measurement combined with engineering practice of coal mining. The coal and rock system model based on the tectonic stress is established. The relationship between energy and scale radius of the coal and rock system is determined to reveal the law of energy accumulation, release, and transfer in the coal and rock system. In view of the characteristics of the porous medium in the coal seam, the measures of water injection are put forward to relieve pressure in the coal seam, and the law of water seepage in the process of water injection in the coal seam is studied based on the seepage mechanics. The result shows that the trend of released energy of damaged coal has good consistency with the variation of permeability, and water injection can reduce the stress concentration and energy concentration of the rock burst system. The engineering practice of the rock burst prevention was taken in Yuejin Coal Mine. The energy characteristics of the coal and rock system in the working face are analyzed, and the measures of water injection and the corresponding parameters are determined.

scholarly journals Numerical Simulation and Engineering Application of Coalbed Water Injection

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Yijie Shi ◽  
Pengfei Wang ◽  
Ronghua Liu ◽  
Xuanhao Tan ◽  
Wen Zhang
Keyword(s):  
Numerical Simulation ◽  
Process Parameters ◽  
Water Injection ◽  
Engineering Application ◽  
Working Environment ◽  
Engineering Practice ◽  
Characteristic Parameters ◽  
Injection Process ◽  
Working Face ◽  
Dust Reduction

Coalbed water injection is the most basic and effective dust-proof technology in the coal mining face. To understand the influence of coalbed water injection process parameters and coalbed characteristic parameters on coal wetting radius, this paper uses Fluent computational fluid dynamics software to systematically study the seepage process of coalbed water injection under different process parameters and coalbed characteristic parameters, calculation results of which are applied to engineering practice. The results show that the numerical simulation can help to predict the wetness range of coalbed water injection, and the results can provide guidance for the onsite design of coalbed water injection process parameters. The effect of dust reduction applied to onsite coalbed water injection is significant, with the average dust reduction rates during coal cutting and support moving being 67.85% and 46.07%, respectively, which effectively reduces the dust concentration on the working face and improves the working environment.

New method of monitoring the transmission range of coal seam water injection and correcting the monitoring results

Measurement ◽  
2021 ◽  
Vol 177 ◽  
pp. 109334
Author(s):  
Jian Chen ◽  
Weimin Cheng ◽  
Gang Wang ◽  
Haomiao Li ◽  
Yanyan Li
Keyword(s):  
Coal Seam ◽  
Water Injection ◽  
New Method ◽  
Transmission Range

scholarly journals The effect of liquid nitrogen cooling on coal cracking and mechanical properties

2018 ◽  
Vol 36 (6) ◽  
pp. 1609-1628 ◽  
Author(s):  
Chengzheng Cai ◽  
Feng Gao ◽  
Yugui Yang
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Acoustic Emission ◽  
Liquid Nitrogen ◽  
Wave Velocity ◽  
Count Rate ◽  
Initial State ◽  
Nitrogen Injection ◽  
Strength Tests ◽  
Liquid Nitrogen Cooling

Liquid nitrogen is a type of super-cryogenic fluid, which can cause the reservoir temperature to decrease significantly and thereby induce formation rock damage and cracking when it is injected into the wellbore as fracturing fluid. An experimental set-up was designed to monitor the acoustic emission signals of coal during its contact with cryogenic liquid nitrogen. Ultrasonic and tensile strength tests were then performed to investigate the effect of liquid nitrogen cooling on coal cracking and the changes in mechanical properties thereof. The results showed that acoustic emission phenomena occurred immediately as the coal sample came into contact with liquid nitrogen. This indicated that evident damage and cracking were induced by liquid nitrogen cooling. During liquid nitrogen injection, the ring-down count rate was high, and the cumulative ring-down counts also increased rapidly. Both the ring-down count rate and the cumulative ring-down counts during liquid nitrogen injection were much greater than those in the post-injection period. Liquid nitrogen cooling caused the micro-fissures inside the coal to expand, leading to a decrease in wave velocity and the deterioration in mechanical strength. The wave velocity, which was measured as soon as the sample was removed from the liquid nitrogen (i.e. the wave velocity was recorded in the cooling state), decreased by 14.46% on average. As the cryogenic samples recovered to room temperature, this value increased to 18.69%. In tensile strength tests, the tensile strengths of samples in cooling and cool-treated states were (on average) 17.39 and 31.43% less than those in initial state. These indicated that both during the cooling and heating processes, damage and cracking were generated within these coal samples, resulting in the acoustic emission phenomenon as well as the decrease in wave velocity and tensile strength.

scholarly journals Effect of Graphene and Carbon Nanotubes on the Thermal Conductivity of WC-Co Cemented Carbide

2019 ◽  
Author(s):  
Kui Chen ◽  
Wenkai Xiao ◽  
Zhengwu Li ◽  
Jiasheng Wu ◽  
Kairong Hong ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Service Life ◽  
Bending Strength ◽  
Cemented Carbide ◽  
Engineering Practice ◽  
Shield Tunneling ◽  
Hardness Tester ◽  
Engineering Costs ◽  
Shield Machine

In recent years, it has been found in engineering practice that the service life of cemented carbide shield machine tools used in uneven soft and hard strata is substantially reduced. The study found that thermal stress is the main reason for the failure of cemented carbide shield tunneling tools when shield tunneling is carried out in uneven soft and hard soil. To maintain the hardness of cemented carbide, improving the thermal conductivity of the shield machine tool is of great importance for prolonging its service life and reducing engineering costs. In this paper, graphene and carbon nanotubes were mixed with WC-Co powder and sintered by SPS (Spark Plasma Sintering). The morphology was observed by using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). A Rockwell hardness tester and bending strength tester were used to test hardness, bending strength and thermal conductivity. The results show that adding trace graphene or carbon nanotubes can increase the bending strength of the cemented carbide by approximately 50% while keeping the hardness of the cemented carbide unchanged. The thermal conductivity of the cemented carbide can be increased by 10% with the addition of 0.12% graphene alone.

scholarly journals Experimental Cryoablation of Thyroid Gland with Propilthiouracyl-Induced Diffuse Hyperplasiae

2021 ◽  
Vol 31 (2) ◽  
pp. 168-179
Author(s):  
Kostiantyn Pobielienskyi ◽  
◽  
Oleksandr Pakhomov ◽  
Gurina Tetyana Gurina Tetyana ◽  
Liliia Pobielienska ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thyroid Gland ◽  
Liquid Nitrogen ◽  
Liquid Nitrogen Temperature ◽  
Freeze Thaw ◽  
Model Experiments ◽  
Endoscopic Control ◽  
The One ◽  
Benign Nodules

Cryoablation under endoscopic control is considered to be a promising approach in therapy of benign nodules of thyroid gland (TG). However, pathologically altered TG tissue differs in thermal conductivity and heat capacity from normal one, therefore the model experiments in animals are necessary to determine the cryoablation parameters. In this research, the changes of temperature during cryoablation of experimental rat TG under normal conditions and the one with propylthiouracil (PTU)-induced diffuse hyperplasia (DH) were comparatively assessed. TG was cryo-ablated in rats, previously received a 0.1% PTU solution within 90 days, using a copper cryoprobe, cooled to liquid nitrogen temperature. The process was controlled using thermocouples placed at different distances from the iceball. Differences between thermograms of intact TG tissue and the samples with PTU-induced DH were established. To achieve the destruction effect of TG with DH to a depth of more than 1 mm, the need of implementing two freeze-thaw cycles with 120-second cryoprobe exposure was proven.

scholarly journals Numerical simulation of magma intrusion on the thermal evolution of low rank coal

2021 ◽  
Author(s):  
Jingyu Jiang ◽  
Ke Zhao ◽  
Yuanping Cheng ◽  
Shaojie Zheng ◽  
Shuo Zhang ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Numerical Simulation ◽  
Coal Seam ◽  
Water Content ◽  
Thermal Evolution ◽  
Low Rank ◽  
Maximum Temperature ◽  
High Water Content ◽  
Low Rank Coal ◽  
Magma Intrusion

Abstract To study the effect of magma intrusion on the thermal evolution of low-rank coal with high water content, the mathematical relationship between water content variation and thermal conductivity of low-rank coal was analyzed by COMSOL Multiphysics numerical simulation and field validation. Taking Daxing Mine in Tiefa coalfield as the research background, the effects of magma finite time intrusion mechanism and water volatilization in coal on thermal evolution and organic maturity of coal seam are investigated in this paper. The results show that as the sill thickness increases, the thermal evolution temperature of the coal seam increases, the required thermal evolution time increases and the final retention temperature increases after the coal seam is cooled down. Approaching the magma, the maximum temperature that the coal seam can reach increases, the maximum temperature lasts longer, and the final temperature retained by the coal seam becomes higher. The increase of water content of coal makes the thermal conductivity increase, and the rate of heat transfer from coal seam is accelerated, and more heat is transferred to distant places in the same time. At the same time, the heat lost by the magma in the same time increases, the time required for the cooling of the magma decreases, and the maximum temperature reached by the underlying coal seam is significantly lower. The presence of moisture weakens the thermal evolution of the magma to the coal seam and reduces the expected maturity of the coal. The results of average random vitrinite reflectance (Ro) and moisture examination of coal samples collected at the Daxing Mine site verified the numerical simulation results of magma thermal evolution.

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